Repeater

ABSTRACT

A relay station is composed of a main reception antenna  1  for receiving both a radio wave of a parent station and a go-around radio wave of a relay station, a subsidiary reception antenna  2  for receiving the go-around radio wave of the relay station, a changeable attenuator  3  and a phase shifting unit  4  for changing an amplitude and phase of a signal received in the subsidiary reception antenna  2 , a composite signal producing unit  5  for producing a composite signal from a signal received in the main reception antenna  1  and the signal sent from the phase shifting unit  4 , an electric power detecting unit  9  for obtaining a composite electric power from a composite voltage extracted in a directivity coupling unit  8 , and a microcomputer  10  for controlling a change of amplitude in the changeable attenuator  3  and a change of phase in the phase shifting unit  4  so as to minimize an average value of the composite electric power obtained in the electric power detecting unit  9.

TECHNICAL FIELD

The present invention relates to a relay device used for terrestrialbroadcasting in which both a reception frequency and a transmissionfrequency having the same value as each other are used.

BACKGROUND ART

In a terrestrial television broadcasting system, a relay device isinstalled in a relay station to send out a broadcast radio wave toregions such as a mountainous region in which it is difficult to receivethe broadcast radio wave. In this relay device, a broadcast radio wavetransmitted from a parent station is received, amplified and again sentout.

Also, the adoption of an orthogonal frequency division multiplex (OFDM)method is determined in Europe and Japan as a transmission method ofdigital terrestrial broadcasting. In this OFDM method, because aplurality of signals having the same frequency as each other can be usedin an area, a single frequency network (SFN) can be used.

Therefore, it is studied to prepare the SFN in the terrestrial digitalbroadcasting, and it is studied to use the reception frequency and thetransmission frequency having the same value as each other in a relaydevice so as to efficiently use the frequency. In cases where thereception frequency and the transmission frequency in a relay device ofa relay station are the same as each other, both a radio wavetransmitted from a parent station and a radio wave transmitted from therelay station are received in a reception antenna of the relay device.In this case, there is a possibility that a signal is oscillated in anamplifying unit of the relay device and a broadcast service cannot beperformed.

To prevent the oscillation of the amplifying unit of the relay device ofthe relay station, it is required that a received electric power D ofthe radio wave received in the parent station and a received electricpower U of a transmission radio wave (or a go-around radio wave) of therelay station satisfy a condition D>U. However, because the electricpower of the radio wave transmitted from the relay device issufficiently higher than the electric power of the radio wave receivedin the relay device, it is not generally easy that the condition D>U issatisfied. Therefore, various methods have been proposed to remove thego-around radio wave and to sufficiently reduce the received electricpower U of the transmission radio wave of the relay station.

As a method of removing the go-around radio wave by using a receptionantenna, a method of canceling-out the go-around radio wave by using aplurality of reception antennas has been proposed. FIG. 1 is a blockdiagram showing the configuration of a conventional relay devicedisclosed in Published Unexamined Japanese Patent Application No.H11-298421 (1999).

In FIG. 1, 1 indicates a main reception antenna for receiving both aradio wave (of a frequency f₁) transmitted from a parent station and ago-around radio wave of a relay station in which the relay device isinstalled. 2 indicates a subsidiary reception antenna for receiving thego-around radio wave of the relay station. 3 indicates a changeableattenuator for changing an amplitude of a reception signal of thego-around radio wave received in the subsidiary reception antenna 2 by apreset attenuation factor. 4 indicates a phase shifting unit (or phaseshifter) for changing a phase of a signal output from the changeableattenuator 3 by a preset shifting phase value. 5 indicates a compositesignal producing unit (or composite signal producer) for producing acomposite signal from both a signal of the radio wave of the parentstation and a signal of the go-around radio wave received in the mainreception antenna 1 and the signal sent from the phase shifting unit 4.6 indicates an amplifying unit for amplifying the composite signalproduced in the composite signal producing unit 5. 7 indicates atransmission antenna for transmitting a transmission radio wave (of thefrequency f₁) of the relay station according to the composite signalamplified in the amplifying unit 6.

Next, an operation will be described below.

The main reception antenna 1 has a directivity in the direction of theparent station, and the radio wave transmitted from the parent stationis received in the main reception antenna 1. Also, a go-around radiowave transmitted from the transmission antenna 7 of the relay station ismixed with the radio wave of the parent station and is received in themain reception antenna 1. A reception signal composed of a mixture ofthe radio wave of the parent station and the go-around radio wave isreceived in the composite signal producing unit 5. The subsidiaryreception antenna 2 is directed towards the transmission antenna 7, andthe go-around radio wave transmitted from the transmission antenna 7 ofthe relay station is received in the subsidiary reception antenna 2. Anamplitude of a reception signal of the go-around radio wave is changedby a preset attenuation factor in the changeable attenuator 3. A phaseof a signal received in the phase shifting unit 4 is changed by a presetshifting phase value, and the signal is output to the composite signalproducing unit 5.

In the composite signal producing unit 5, a composite signal is producedfrom a signal of a mixture of the radio wave of the parent station andthe go-around radio wave received in the main reception antenna 1 and asignal of the go-around radio wave which is received in the subsidiaryreception antenna 2 and of which the amplitude and the phase areadjusted. In this case, the attenuation factor of the changeableattenuator 3 and the shifting phase value of the phase shifting unit 4are set so as to produce a composite signal from a signal of thego-around radio wave received in the main reception antenna 1 and asignal of the go-around radio wave received in the subsidiary receptionantenna 2 having the same amplitude as each other at phases opposite toeach other. Therefore, the signal of the go-around radio wave iscanceled out in the composite signal, and the output of the compositesignal producing unit 5 is composed of the composite signal of only theradio wave component of the parent station.

Because the conventional relay device has the above-describedconfiguration, when characteristics of the main reception antenna 1, thesubsidiary reception antenna 2 and/or the transmission antenna 7 arechanged due to a change of the environment caused by wind, snow or thelike, the two go-around radio waves received in the composite signalproducing unit 5 do not have the same amplitude as each other at thephases opposite to each other. Therefore, a problem has arisen that thego-around radio wave cannot be completely removed from the compositesignal.

Also, in cases where the conventional relay device is set so as to beautomatically adapted for the change of the environment, it is requiredto distinguish the go-around radio wave from the radio wave of theparent station. Therefore, as is described in the patent application,another problem has arisen that it is required to superpose a relaystation identification signal on the transmission radio wave of therelay station transmitted from the transmission antenna 7.

The present invention is provided to solve the above-described problem,and the object of the present invention is to provide a relay device inwhich a go-around radio wave can be canceled out without thesuperposition of a relay station identification signal while beingadapted for a change of the environment caused by wind or snow.

DISCLOSURE OF THE INVENTION

A relay device according to the present invention, in which a radio waveof a parent station is received and amplified and a transmission radiowave having the same frequency as that of the radio wave of the parentstation is transmitted, comprises a main reception antenna for receivingboth the radio wave of the parent station and a go-around radio wave ofa relay station, a subsidiary reception antenna for receiving thego-around radio wave of the relay station, a changeable attenuator forchanging an amplitude of a signal of the go-around radio wave receivedby the subsidiary reception antenna, a phase shifter for changing aphase of the signal of the go-around radio wave received by thesubsidiary reception antenna, a composite signal producer for producinga composite signal from a signal of the radio wave of the parent stationreceived by the main reception antenna, the signal of the go-aroundradio wave of the relay station and the signal of which the amplitude ischanged by the changeable attenuator and the phase is changed by thephase shifter, a directivity coupler for extracting a composite voltageof the composite signal output from the composite signal producer, anelectric power detector for obtaining a composite electric power fromthe composite voltage extracted by the directivity coupler, and amicrocomputer for controlling both a change of the amplitude performedby the changeable attenuator and a change of the phase performed by thephase shifter so as to minimize an average value of the compositeelectric power obtained by the electric power detector.

Therefore, the go-around radio wave can be cancelled while the relaydevice is adapted for a change of an environment of the relay device.

The relay device according to the present invention further comprises anoutput controller for controlling an output of the transmission radiowave transmitted from the relay station according to an instruction ofthe microcomputer when the supply of an electric power is started.

Therefore, the oscillation occurring in the relay device can besuppressed when the supply of an electric power to the relay device isstarted.

In the relay device according to the present invention, an initialoperation point of the changeable attenuator and an initial operationpoint of the phase shifter are automatically detected by themicrocomputer by obtaining a minimum value of the composite electricpower obtained by the electric power detector.

Therefore, the detection of initial operation points of both thechangeable attenuator and the phase shifter performed by measuring theamplitude and phase of the go-around radio wave is not required.

The relay device according to the present invention further comprises anoutput controller for controlling an output of the transmission radiowave transmitted from the relay station according to an instruction ofthe microcomputer when an initial operation point of the changeableattenuator and an initial operation point of the phase shifter areautomatically detected by the microcomputer.

Therefore, the oscillation occurring in the relay device can besuppressed during the automatic detection of the initial operationpoints performed by the microcomputer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the configuration of a conventionalrelay device.

FIG. 2 is a block diagram showing the configuration of a relay deviceaccording to a first embodiment of the present invention.

FIG. 3 is a view showing a characteristic of a change of an averagevalue of a composite electric power due to a change of an attenuationfactor of a changeable attenuator according to a second embodiment ofthe present invention.

FIG. 4 is a view showing a characteristic of a change of an averagevalue of a composite electric power due to a change of a value of aphase shifted in a phase shifting unit according to the secondembodiment of the present invention.

FIG. 5 is a block diagram showing the configuration of a relay deviceaccording to a third embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the best mode for carrying out the present invention willnow be described with reference to the accompanying drawings to explainthe present invention in more detail.

Embodiment 1

FIG. 2 is a block diagram showing the configuration of a relay deviceaccording to a first embodiment of the present invention. In FIG. 2, 8indicates a directivity coupling unit (or directivity coupler) forextracting a composite voltage of the composite signal output from thecomposite signal producing unit 5. 9 indicates an electric powerdetecting unit (or electric power detector) for obtaining a compositeelectric power from the composite voltage extracted in the directivitycoupling unit 8. 10 indicates a microcomputer for controlling anattenuation factor of the changeable attenuator 3 and a shifting phasevalue of the phase shifting unit 4 so as to minimize an average value ofthe composite electric power obtained in the electric power detectingunit 9. The other constitutional elements are the same as or equivalentto those of the conventional relay device shown in FIG. 1.

Next, an operation will be described below.

A composite voltage output from the composite signal producing unit 5 isextracted in the directivity coupling unit 8, a composite electric poweris obtained in the electric power detecting unit 9 from the compositevoltage extracted in the directivity coupling unit 8, and the compositeelectric power is input to the microcomputer 10.

A voltage V_(M1) of a radio wave of a parent station received in themain reception antenna 1 is expressed according to an equation (1).V _(M1) =V _(d) f(t)  (1)In this case, a voltage V_(M2) of a go-around radio wave received in themain reception antenna 1 is expressed according to an equation (2).V _(M2) =V _(U1) e ^(iθ1) f(t−Δt)  (2)Here, V_(d) denotes an average voltage of the radio wave of the parentstation, V_(U1) denotes an average voltage of the go-around radio wavereceived in the main reception antenna 1, θ1 denotes a phase of thego-around radio wave received in the main reception antenna 1, and Δtdenotes a time period from the reception of the radio wave of the parentstation to the reception of the go-around radio wave in the mainreception antenna 1 or the subsidiary reception antenna 2 through theprocessing of the radio wave in the relay device and the transmission ofthe go-around radio wave from the transmission antenna 7. In case of atelevision relay device, the time period Δt is normally equal to orhigher than 1 μs.

In the same manner, a voltage V_(s2) of a go-around radio wave receivedin the subsidiary reception antenna 2 is expressed according to anequation (3).V _(s2) =V _(U2) e ^(iθ2) f(t−Δt)  (3)Here, V_(U2) denotes an average voltage of the go-around radio wavereceived in the subsidiary reception antenna 2, and θ2 denotes a phaseof the go-around radio wave received in the subsidiary reception antenna2.

Therefore, the voltage V_(N) received in the main reception antenna 1 isexpressed according to an equation (4).V _(M) =V _(M1) +V _(M2) =V _(d) f(t)+V _(U1)e^(jθ1) f(t−Δt)  (4)

In cases where an amplitude of a signal corresponding to the voltageV_(s2) of the go-around radio wave received in the subsidiary receptionantenna 2 is changed by α times (or an attenuation factor α) in thechangeable attenuator 3 and a phase of the signal of the voltage V_(s2)is changed by φ (or a shifting phase value φ) in the phase shifting unit4, an composite voltage V₀ output from the composite signal producingunit 5 is expressed according to an equation (5).V ₀ =V _(d) f(t)+(V _(U1) e ^(jθ1) +αV _(U2) e ^(j(θ2+φ)))f(t−Δt)  (5)

Thereafter, the composite voltage V₀ is squared in the electric powerdetecting unit 9 to obtain a composite electric power.V₀ ² =V _(d) ² f ²(t)+(V _(U1) e ^(jθ1) +αV _(U2) e ^(j(θ2+φ)))² f²(^(t−Δt))+2V _(d)(V _(U1) e ^(jθ1) +αV _(U2) e^(j(θ2+φ)))f(t)f(t−Δt)  (6)Here, when the condition Δt>1 μs is satisfied, an average of f(t)f(t−Δt) is equal to 0 due to the characteristics of the OFDM method ofthe terrestrial digital broadcasting. Therefore, an average value of thecomposite electric power is obtained according to an equation (7).|V ₀ ² |=|V _(d) ² f ²(t)|+|(V _(U1) e ^(jθ1) +αV _(U2) e ^(j(θ2+φ)))² f²(t−Δt)|  (7)Here, |a| denotes an average of the symbol “a”. In this case, it isapplicable that the average value |V₀ ²| of the composite electric powerbe obtained in the electric power detecting unit 9 and be output to themicrocomputer 10. Also, it is applicable that the average value |V₀ ²|of the composite electric power be obtained in the microcomputer 10.

Also, to cancel the go-around radio wave, the attenuation factor α ofthe changeable attenuator 3 is set according to an equation (8).V _(U1) =αV _(U2) →α=V _(U1) /V _(U2)  (8)Also, the shifting phase value φ of the phase shifting unit 4 is setaccording to an equation (9).θ2 +φ=θ1+π→φ=θ1−θ2+π  (9)When the condition of the equation (9) is satisfied,e ^(j(θ2+φ)) =e ^(j(θ1+π)) =e ^(jθ1) e ^(jπ) =−e ^(jθ1)is obtained. Also, when the condition of the equation (8) is satisfied,the second term of the equation (7) is equal to 0. Therefore, it isrealized that the go-around radio wave is canceled out in the compositevoltage output from the composite signal producing unit 5.

As is described above, in cases where the attenuation factor α of thechangeable attenuator 3 and the shifting phase value φ of the phaseshifting unit 4 are set as operation points of both the changeableattenuator 3 and the phase shifting unit 4 so as to minimize the averagevalue |V₀ ²| of the composite electric power, it is realized that therelay device is set to a state of the canceling-out of the go-aroundradio wave.

Accordingly, in the first embodiment, in cases where the environment ofthe relay device is changed due to wind or snow, the attenuation factorof the changeable attenuator 3 and a degree of phase shifted in thephase shifting unit 4 are controlled by the microcomputer 10 so as tominimize the average value |V₀ ²| of the composite electric power.Therefore, the go-around radio wave can be canceled out while beingadapted for a change of the environment. Also, in this algorithm, it isnot required to superpose a relay device identification signalidentifying the go-around radio wave on the transmission radio wave ofthe relay station.

Embodiment 2

In the first embodiment, on the assumption that initial operation pointsof both the changeable attenuator 3 and the phase shifting unit 4 areset when the relay device is installed in the relay station, the relaydevice is operated while being adapted for a change of the environment.However, it is possible to automatically obtain the initial operationpoints.

FIG. 3 is a view showing a characteristic of a change of the averagevalue |V₀ ²| of the composite electric power due to a change of theattenuation factor α of the changeable attenuator 3. As shown in FIG. 3,a change of the average value |V₀ ²| of the composite electric powerwith respect to the attenuation factor α of the changeable attenuator 3is expressed by a quadratic curve, and an operation point correspondingto the canceling-out of the go-around radio wave is placed at a point ofFIG. 3 at which the average value |V₀ ²| of the composite electric poweris minimized. Therefore, when the supply of an electric power to therelay device is started, the minimum point of the average value |V₀ ²|of the composite electric power is detected while changing theattenuation factor α little by little by using the microcomputer 10.

FIG. 4 is a view showing a characteristic of a change of the averagevalue |V₀ ²| of the composite electric power due to a change of thevalue φ of the phase shifted in the phase shifting unit 4. As shown inFIG. 4, a change of the average value |V₀ ² | of the composite electricpower with respect to the shifting phase value φ is expressed by acosine curve, and an operation point corresponding to the canceling-outof the go-around radio wave is placed at a point of FIG. 4 at which theaverage value |V₀ ²| of the composite electric power is minimized.Therefore, in the same manner as in the above case, the minimum point ofthe average value |V₀ ²| of the composite electric power is detectedwhile changing the phase shifting value φ little by little by using themicrocomputer 10.

As is described above, in the second embodiment, the initial operationpoint, at which the average value |V₀ ²| of the composite electric poweris minimized, can be automatically detected. Therefore, when the relaydevice is installed in the relay station, it is not required to setoperation points of both the changeable attenuator 3 and the phaseshifting unit 4 by measuring the amplitude and phase of the go-aroundradio wave.

Embodiment 3

In the first embodiment, when the relay device is installed in the relaystation, the initial operation points of both the changeable attenuator3 and the phase shifting unit 4 are measured and set. However, when thesupply of an electric power to the relay device is suddenly started, thego-around radio wave cannot be sufficiently canceled out due tomeasurement errors of the initial operation points. Therefore, there isa probability that a signal oscillation occurs in the relay device.

Also, in the second embodiment, the initial operation points of both thechangeable attenuator 3 and the phase shifting unit 4 are automaticallydetected by the microcomputer 10. However, the go-around radio wavecannot be sufficiently canceled out during the detection of the initialoperation points. Therefore, in the same manner, there is a probabilitythat a signal oscillation occurs in the relay device.

FIG. 5 is a block diagram showing the configuration of a relay deviceaccording to a third embodiment of the present invention. In FIG. 5, 11indicates an output control unit (or output controller) for controllingan output of the amplifying unit 6 by using the microcomputer 10 andoutputting the output of the amplifying unit 6 to the transmissionantenna 7.

Next, an operation will be described below.

When the supply of an electric power to the relay device is started, anoutput of the output control unit 11 is set to zero under the control ofthe microcomputer 10 to control the relay device not to output atransmission radio wave from the relay device. In this case, an outputvalue of the electric power detecting unit 9 is stored in themicrocomputer 10. Because no go-around radio wave is included in thisoutput value of the electric power detecting unit 9, the output valueindicates a reception level of the radio wave of the parent station.Thereafter, the output control unit 11 is controlled by themicrocomputer 10 so as to heighten an output level (or output value) ofthe relay device little by little until the output level of the relaydevice reaches a regular output level. Therefore, a signal oscillationoccurring in the relay device can be avoided.

In this case, a threshold value is preset to a value ranging from theoutput value stored in the microcomputer 10 to the double of the outputvalue. When an electric power detected in the electric power detectingunit 9 is equal to or higher than the preset threshold value, operationpoints set in both the changeable attenuator 3 and the phase shiftingunit 4 differ from optimum operation points at which the average value|V₀ ²| of the composite electric power is minimized. Therefore, theelectric power equal to or higher than the preset threshold valueindicates that the go-around radio wave is not canceled out. In thiscase, an output of the relay device is fixed at the operation pointsunder the control of the output control unit 11, the optimum operationpoints are detected in the same manner as in the case of the change ofthe environment, and the output of the relay device is graduallyheightened.

Also, while the initial operation points of both the changeableattenuator 3 and the phase shifting unit 4 are automatically detected byusing the microcomputer 10, the output level of the output control unit11 is fixed to an appropriate level, which is equal to or lower thanhalf of the regular output level, according to an instruction sent fromthe microcomputer 10. In this case, because an oscillation condition forthe relay device is not satisfied, a signal oscillation occurring in therelay device can be avoided.

As is described above, in the third embodiment, an output level of therelay device is controlled by the output control unit 11 according tothe control of the microcomputer 10. Therefore, when the supply of anelectric power to the relay device is started or initial operationpoints are automatically detected by the microcomputer 10, theoscillation occurring in the relay device can be suppressed.

INDUSTRIAL APPLICABILITY

As is described above, in a relay device according to the presentinvention, a transmission radio wave having the same frequency as thatof a radio wave received from a parent station is transmitted.Therefore, the relay device is appropriate to the canceling-out of ago-around radio wave while being adapted for a change of an environmentof the relay device caused by wind or snow.

1. A relay device, in which a radio wave of a parent station is receivedand amplified and a transmission radio wave having the same frequency asthat of the radio wave of the parent station is transmitted, comprising:a main reception antenna for receiving both the radio wave of the parentstation and a go-around radio wave of a relay station; a subsidiaryreception antenna for receiving the go-around radio wave of the relaystation; a changeable attenuator for changing an amplitude of a signalof the go-around radio wave received by the subsidiary receptionantenna; a phase shifter for changing a phase of the signal of thego-around radio wave received by the subsidiary reception antenna; acomposite signal producer for producing a composite signal from a signalof the radio wave of the parent station received by the main receptionantenna, the signal of the go-around radio wave of the relay station andthe signal of which the amplitude is changed by the changeableattenuator and the phase is changed by the phase shifter; a directivitycoupler for extracting a composite voltage of the composite signaloutput from the composite signal producer; an electric power detectorfor obtaining a composite electric power from the composite voltageextracted by the directivity coupler; and a microcomputer forcontrolling both a change of the amplitude performed by the changeableattenuator and a change of the phase performed by the phase shifter soas to minimize an average value of the composite electric power obtainedby the electric power detector.
 2. A relay device according to claim 1,further comprising: an output controller for controlling an output ofthe transmission radio wave transmitted from the relay station accordingto an instruction of the microcomputer when the supply of an electricpower is started.
 3. A relay device according to claim 1, wherein aninitial operation point of the changeable attenuator and an initialoperation point of the phase shifter are automatically detected by themicrocomputer by obtaining a minimum value of the composite electricpower obtained by the electric power detector.
 4. A relay deviceaccording to claim 1, further comprising: an output controller forcontrolling an output of the transmission radio wave transmitted fromthe relay station according to an instruction of the microcomputer whenan initial operation point of the changeable attenuator and an initialoperation point of the phase shifter are automatically detected by themicrocomputer.